A conventional belt winder, as is known from U.S. Pat. No. 5,593,105, comprises a frame in which a belt spool is rotatably mounted, which is provided with locking toothing, a locking catch provided with at least one locking tooth, which locking catch can be moved into the locking toothing in order to lock the belt spool against a rotation in the unwinding direction of the safety belt, as well as a control ring rotatable relative to the belt spool, which ring is provided with coupling toothing and engages on the locking catch, and a coupling catch rotatably mounted on the belt spool and a control disc which is rotatable relative to the belt spool and on rotation relatively to the belt spool brings the coupling catch into engagement with the coupling toothing of the control ring, whereby on rotation of the belt spool in the unwinding direction, the control ring is entrained via the coupling catch and the locking catch is engaged into the locking toothing up to a first contact between the locking tooth and the locking toothing, from this first contact such a moment of rotation being exerted from the locking toothing onto the locking catch that the locking catch is pivoted completely into the locking toothing.
A belt winder of this type serves to make available a vehicle safety belt for an occupant of a vehicle, in which the safety belt in the normal state is able to be unwound freely from the belt spool against the force of a return spring, whilst in the locked state a belt webbing withdrawal is not possible. The locking can either take place in a manner which is sensitive to the belt webbing, i.e. as a function of accelerations acting on the belt webbing, or in a manner which is sensitive to the vehicle, i.e. as a function of accelerations acting on the vehicle.
In such belt winders, however, an undesired locking of the belt spool can occur. This can happen when the belt webbing, on unwinding from the belt spool or on winding thereon, is suddenly braked or accelerated, for example by arresting an insertion tongue situated on the belt webbing, on a guide of the safety belt or a deflection mounting, with an alteration of the adjustment of a vertically adjustable deflection mounting or at the end of the winding movement when the belt webbing is drawn tight. In such situations, it can happen that the locking of the belt winder is initiated in a manner which is sensitive to the belt webbing. The belt winder then arrives into a state in which the locking mechanism, sensitive to the belt webbing, is activated, whilst at the same time the belt webbing acts upon the belt spool in the unwinding direction. This situation can only be eliminated with increased effort, for example by powerful pulling on the belt webbing, so that a belt webbing slack is produced, and subsequent freeing of the belt webbing, so that the belt spool can rotate under the force of the return spring in the winding direction, whereby the locking mechanism is freed and can return into its position of rest. This situation is further intensified if at the same time as the activation of the locking mechanism, sensitive to the belt webbing, also the locking of the belt winder, sensitive to the vehicle, is initiated, for example by vibrations of the vehicle or by engagement of a back seat rest which is able to be folded and is provided with a belt winder, in its locking mechanism. In this case, the belt winder can arrive into a state in which both the belt webbing-sensitive and also the vehicle-sensitive locking mechanism of the belt winder is tensioned in activated state.